Japanese Patent Application, First Publication No. Hei 7-187072 discloses art relating to an automatic control method for a submersible unit using neural networks. This automatic control method for a submersible unit absorbs the effects of periodic external forces (external disturbances to the positional control of the submersible unit) such as waves by using learning control employing conventionally used proportional-plus-integral-plus-derivative control (PID control) and neural networks, thereby holding the diving position of the submersible unit constant even when periodic external forces are applied. That is, according to this automatic control method, the frequencies of periodic disturbances due to waves and the like are learned, an oscillator network is provided for outputting a sine wave signal of a standard frequency based on the learned frequency, and a neural controller controls the depth of the submersible unit based on the output of the oscillator network.
However, although the above-described automatic control method for a submersible unit is capable of holding the depth constant by absorbing the effects of periodic external disturbances acting on the submersible unit based on a sine wave output from an oscillator network, it is not capable of holding the depth sufficiently constant with respect to non-periodic external disturbances.